This invention relates generally to motor control and particularly to a system for accurately orienting a member being rotated by a motor.
The screen of a color picture tube is composed of triads of phosphors which emit different colored light when excited by electrons. Typically, the screen is composed of alternating stripes or circular dots of phosphors which respectively emit red, green and blue light. Positioned between the screen and the electron gun from which the exciting electrons emanate, is an apertured color selection electrode, commonly called a shadow mask. The shadow mask assures that the electron beams excite stripes or dots of the proper color.
During the production of the phosphor screen, a faceplate panel is placed in a rotating carrier. A slurry containing the phosphor is fed onto the panel and the rotation causes the slurry to uniformly coat the entire interior surface of the panel. During the rotation, the panel moves along a conveyor system while the slurry spreads across the surface of the panel, and excess slurry is poured from the panel. The shadow mask is inserted into the panel and the panel is placed upon a lighthouse where the phosphor is exposed to light through the apertures within the shadow mask.
The trend in the production of color picture tubes is that of automating the equipment used to produce and handle the various parts from which the color picture tubes are made. Automatic production systems typically include a programmable computer to control the transfer and production equipment and also to keep track of the sizes and types of parts being processed. An example of an automated system, for producing color picture tube screens is described in U.S. Pat. No. 4,370,036 issued to W. R. Kelly on Jan. 25, 1983. Typically in automatic systems, parts being transferred from one position to another, or being processed, must be arranged at a specific position and in a particular orientation. For this reason, there is a need for a system for accurately stopping the rotating carriers so that the panels carried by the carriers are in a predetermined orientation whereby the panels can be removed from the carriers by automatic equipment. The present invention fullfills this requirement.